Typical integrated circuit devices contain multiple printed circuit layers. Each layer is insulated from its adjacent layer except where interlayer connections are selectively created. The individual circuit layers of an integrated circuit device are typically created by a photolithographic process. Each layer is formed on an integrated circuit device during a separate trip through the photolithographic manufacturing area. After each trip, the integrated circuit device is transported to other manufacturing areas where additional processing steps, such as etching and deposition, are performed. Thereafter, the integrated circuit device is returned to the photolithographic process manufacturing area so that an additional circuit layer may be applied. The process is then repeated until the desired number of circuit layers has been created.
During the manufacture of integrated circuit devices, several devices are typically formed on a single silicon substrate which is commonly referred to in the industry as a “wafer”. A single wafer may, for example, contain well over 100 integrated circuit devices. When the manufacture of the integrated circuit devices on a wafer is completed, the wafer is sawn apart such that the integrated circuit devices contained thereon are separated into individual units.
During the wafer manufacturing process, it is often desirable to tightly control various parameters of the integrated circuit devices, or portions thereof. For example, many integrated circuit devices are required to generate an accurate reference voltage. To be accurate requires precise control of two or more process values and precise matching in the critical components that generate the reference voltage. This level of control and matching is often not practical to achieve. Therefore, an alternative approach is needed.
The most popular alternative approach is a method known as “trim”. Trim allows process values of the components to be changed after wafer manufacture. The values are changed to set the reference voltage very close to the ideal target. The agent of change may, for example, take the form of shorting diodes to lower resistance, opening fuse links to increase resistance, or laser cutting resistors to increase resistance.